I also have a similar side project planned for a revamp. Successfully made a v1 with grease monkey (vanilla JS) + stylish back in maybe 2016. Super dangerous to keep firefox 56 running only for this front-end. Just need to do the v2 then migrate to latest librewolf.

I want to redo the whole thing in Vue, client side routing with build step. The problem is that

• site is not open source
• no API doc (but I already made my own)
• required log-in (no sensitive info)
• some route request must be made from that domain due to CORS

My goal is not to change the UI but wipe the whole page and start over with custom API call instead. V1 do this by visiting a 404 route to stop unnecessary load and use my own URL param for the API call. For bonus cringe I used local storage for database.

Ended up having to use userscript, and now I'm kinda stuck with how to mash Vite build and tamper/violent monkey together :(
Do you have any suggestion or resource I can learn more on this?